Conventional systems for a direct injection of fuel into the combustion chamber of an internal combustion engine are commonly known. A distinction is made in this context between "stratified" mode as a first operating mode, and "homogeneous" mode as a second operating mode. Stratified mode is used in particular at lower loads, while homogeneous mode is utilized when larger loads are present at the internal combustion engine. In stratified mode, the fuel is injected during the compression phase of the internal combustion engine into the combustion chamber, specifically into the immediate vicinity of a spark plug therein. The result is that uniform distribution of the fuel in the combustion chamber can no longer occur. The advantage of stratified mode is that the smaller loads that are present can be handled by the internal combustion engine with a very small fuel mass. Stratified mode is not sufficient, however, for greater loads. In the homogeneous mode provided for such greater loads, the fuel is injected during the intake phase of the internal combustion engine, so that turbulent flow and thus distribution of the fuel in the combustion chamber can still readily occur. To this extent, homogeneous mode corresponds approximately to the operation of internal combustion engines in which fuel is injected conventionally into the intake duct.
In both operating modes, i.e. in stratified and in homogeneous mode, the fuel mass to be injected is controlled and/or regulated by a control device, as a function of a plurality of input variables, to a value that is optimal in terms of fuel economy, emissions reduction, and the like. This control and/or regulation depends, among other things, on a reference torque that is calculated by the control device. The reference torque represents the total torque to be delivered by the internal combustion engine, i.e. the torque which the internal combustion engine is intended to generate. This reference torque is made up, among other things, of the torque requested by the driver and optionally of other torque requirements, for example of a climate-control system or the like. The torque requested by the driver is derived from the position of the accelerator pedal actuated by the driver.
It is possible, however, that a fault may occur in the calculation, by the control device, of the reference torque from the aforesaid input variables. This may involve a fault of a sensor and/or of the control device and/or the like. In particular, it may involve a software fault in the control device which, because the fault occurs infrequently, has not hitherto been detected.
It is the object of the present invention to create a method with which a fault in the calculation of the reference torque can be detected.